Separation of magnetizable particles

ABSTRACT

Apparatus and process for the removal of magnetizable particles during grinding of material containing such particles, e.g. grinding of iron-containing titanium ores or slag. The titanium ore, for example, is ground, ground material is pneumatically conveyed to a separator from whence the fines are withdrawn to be treated in conventional manner. The coarse material is subjected to magnetic attraction to remove magnetizable particles and the balance is recycled for further grinding.

United States Patent 11 1 1 1 ,754,713

Kienast et al. 1 Aug. 28, 1973 SEPARATION OF MAGNETIZABLE 2,990,1246/1961 Cavanagh et al. 241/24 1,619,295 3/1927 Gardner 241/19 PARTICLES2,962,231 11/1960 Weston 241/24 [75] Inventors: Gerhard Kienast;Herlbert Stutgens; 3,397, 45 3 1968 Muller 241 54 x Hans-Gunter Zander,all of 2,811,434 10/1957 Moklebust 75/30 Krefeld, Germany 3,218,15211/1965 Sasabe 75/1 [73] Assignee: Bayer Aktlengesellschaft,

Leve k Germany Primary Examiner-Granville Y. Custer, Jr. Pl d M 17 1971Attorney-Burgess, Dinklage & Sprung 1e ar.

21 A l. N 125,149 1 pp [57 ABSTRACT 30] Foreign Application priority mApparatus and process for the removal of magnetizable Mar 28 1970 GermanP 20 15 073 6 particles during grinding of material containing such yparticles, e.g. grinding of iron-containing titanium ores {52] Us Cl241/24 or slag. The titanium ore, for example, is ground, 5 l 1 4/00ground material is pneumatically conveyed to a separa- [58] Fieid 24 3O52 tor from whence the fines are withdrawn to be treated 41/54 1, inconventional manner. The coarse material is subjected to magneticattraetion to remove magnetizable [56] References Cited particles andthe balance is recycled for further grind- UNITED STATES PATENTS3,291,398 12/1966 Weston et al 241/19 X 5 Claims, 1 Drawing Figure A 6 ra,

Patented Aug. 28, 1973 3,754,713

INVENTORS:

GERHARD KIENAST, HERIBERT STUTGENS, HANS GUNTHER ZANDER.

SEPARATION OF MAGNETIZABLE PARTICLES This invention relates to a processfor the separation of magnetizable particles, i.e. particles which areattracted by a magnet, from crushed material during the grindingoperation.

In the dressing of ores, the components to be recovered are separatedfrom the unwanted components, e.g. from the rock material, during thedressing and enrichment Stages from the unwanted components, for examplefrom the rock material, by means of one or more separation processes.Since the ores to be processed in practice, for example iron ores, are,however, almost exclusively highly heterogeneous mixtures of differentminerals, clean separation between the rock material and the pure ore isdifficult and, for this reason, it is frequently necessary to useseveral separation processes in succession in order to obtain a usefulresult.

Accordingly, several techniques in which magnetic separators are usedhave already been proposed for dressing ores, above all ores of the kindcontaining iron oxides. The function of these magnetic separators is toseparate magnetic components, for example metallic iron or magnetic ormagnetizable oxides from'the slag or the rock material. So far as thefirst of these cases is concerned, the following processes for examplehave been used: the Krupp-Eisenschamm process, the Krupp-Renn process,the SL-RN process and the Esso Fior process (cf. Gmelin-Durrer.Metallurgie des Eisens, 4th Edition, 1968, Vol. 20, page 324 et seq andVol. 28, pages I37 et seq).

In these processes, the material which has generally been subjected to areducing treatment is first sifted and then passed over magneticseparators to separate the metallic iron. In some cases, sifting ispreceded by an initial size-reduction stag e. Unfortunately,all theseprocesses have the disadvantage that, due to the coarse particles stillpresent, a relatively large proportion of magnetizable material remainsentrained by the non-magnetizable material. w

One exceptional method of dressing is used in the production of titaniumslags (cf. Barksdale, Titanium, 2nd Edition, 1966 pp. 201-212). In thiscase, ilmenite is reduced with carbon to give, in addition to iron, avaluable titanium slag which is used in the production of titaniumdioxide pigments. The iron normally accumulates in the form ofa meltwhich can be run off. Relatively coarse, exposed iron particles leftbehind in the size-reduced slag are removed by magnetic separators.However, the smaller iron particles which are still enveloped in thetitanium slag are not entrained in this way and are left behind in theslag. They makeup approximately 1 percent by weight of the slag.However, this proportion of metallic iron can promote unwanted reactionsduring subsequent further processing of the titanium slag.

It is accordingly an object of the invention to provide a process andapparatus for removing magnetizable material from material in which itis embedded.

It is a further object of the invention to provide a process andapparatus for removing iron from coarsegrained titanium materialscontaining iron.

These and other objects and advantages are realized in accordance withthe present invention which provides an apparatus and process by whichit is possible to separate magnetizable particles from a material in thecourse of size-reduction during the grinding operation and in which,after grinding the material is separated into fine material and gravelby centrifugal air separation, and the following separation of themagnetizable particles by a magnetic separator, the gravellike materialis returned to the grinding operation.

The process according to the invention can be used with advantage duringthe dressing of materials which on the one hand contain magnetic ormagnetizable components and which on the other hand have to be subjectedto a size-reduction operation for dressing. For example, mixed orescontaining magnetic or magnetizable constituents can be separated anddressed by this process. The process according to the invention is alsosuitable for enriching titanium-containing materials such as for examplerutile or ilmenite. Thus, the process can be used for example toseparate two minerals occurring naturally alongside one another, as isthe case for example with the non-magnetic rutile and the weaky magneticilmenite. It is possible in this way to remove the last traces ofmetallic iron from titanium slags of the kind obtained by reducingilmenite with carbon. In principle, only a size-reducing machine, amachine for separating coarse and fine material and a magnetic separatorare required for carrying out the process.

Size-reduction of the material is generally carried out in grindingmachines, for example hammer mills, centrifugal mills, pounding mills,disc attrition mills, pendulum mills, ball mills, tube mills, wet mills,percussion mills or vibration' mills. Tubular mills or ball mills areparticularly suitable. The grain size of the material discharged fromthe mill in the process according to the invention should best bebetween about 5 microns and 400 microns.

Separation into fine material and gravel can be carried out for examplein sifting machines or separators. Separators such as for examplecentrifugal separators, centrifugal air separators or reversingseparators, are particularlysuitable. The size-reduced material canactually be pre-separatred in the'mill itself by means of a stream ofair circulating inside it. Depending upon the intensity of the airstream flowing through the mill, a material of suitable grain sizedistribution is discharged from the mill. This material passes with thecarrier air into a separator in which it is separated into fine material and gravel. By suitably establishing the conditions for thecentrifugal or flow separator to be used, for example, it is possibleaccurately to adjust the grain-size limit between fine material andgravel for the particular grain sizes requires. At the same time, a highdegree of sharpness in separation is obtained. Depending upon thesetting of the separator, the grain size of the fine material is betweenabout 5 and microns and the grain size of the gravel is accordinglybetween about 30 and 400 microns, the fine material and gravel beingseparated with sufficient definition at a corresponding grain size whichis between about 30 and I20 microns.

In addition to the coarse-grained particles, the particlesof higherspecific gravities are also enriched to a considerable extent in thegravel. Due to their inferior grinding properties and their greaterdensity, the ore components are predominant in the gravel in the workingup of minerals, whereas the iron is predominant in the gravel in theworking up of reduced materials. The components enriched in this way inthe gravel are then separated by means of magnetic separators.Separation into fine material and gravel can be carried out eithercontinuously or in stages. The materials to be dressed may be wet canactually be dried in the same installation by heating the air streamwith a hot gas introduced into it, as is done in conventional combinedgrinding and drying machines. This makes magnetic separation mucheasier, above all in cases where strong magnetic fields are used.

Both weak magnetic field separators and also strong magnetic fieldseparators can be used as the magnetic separators. The weak-fieldmagnetic separators have the best separating effect, their superiorityincreasing with decreasing grain size.

A preferred embodiment of the process according to the invention isdescribed in the accompanying drawing which is a schematic flow sheet ofa process for the dressing of titanium slag.

in the FIGURE, the reference 1 denotes a feed hopper, the reference 2 arotary-table feeder, the reference 3 a ball valve, the reference 4 atubular mill, the reference 5 a separator, the reference 6 a gravelreturn to a magnetic separator 7, the reference 8 the surface of a drum,the reference 9 a brush roller, the reference 10 a pipe to a supplycontainer 11, the reference 12 a return screw for the gravel, thereference 13 a feed pipe, the reference 14 a cyclone separator, thereference 15 a conveyor screw and the reference 16 a supply to acontainer for fine material; 17 is a fan, 18 a dust filter and 19 and 20are feed pipes.

From the supply hopper l, the crude material runs continuously throughthe rotary-table feeder 2 and the ball valve 3 into the tubular mill 4which is partly filled with steel balls of different diameter. The crudematerial is then ground by rotation of the mill. By means of a vigorousair stream which is passed through the mill, material which has alreadybeen size-reduced therein is pre-separated and delivered pneumaticallyto the separator 5. The coarser-grained and specifically heaviermaterial is separated in the form of gravel in known manner in theseparator 5. Through the exact setting of the fittings in the separatorand by carefully maintaim ing the rates of air flow, the grain sizelimit at which separation between fine material and gravel is to takeplace is determined with precision. The gravel passes as return feed 6to the magnetic separator 7 where the material to be separated isscattered on to the magnetically induced and rotating drum surface 8.Whereas the material which is not to be magnetized is immediatelyrepelled by the rotating drum and then carried back into the mill by thegravel return screw 12, the magnetizable material temporarily adheres tothe drum and is removed from the drum at the opposite side by a brushroller 9. The magnetizable constituents obtained are continuouslydelivered through the feed pipe 10 to a container 11.

The fine material 13 separated in the separator (the oxidic constituentsin the reduction of ore, the rock material in the dressing of ore) isseparated from the carrier air in a cyclone separator 14 and introducedby the conveyor screw 15 into the fine material supply line 16 fortransport to a container (not shown). The carrier air is drawn away bythe mill fan 17, some of it being returned to the mill system. The restof the air passes through the dust filter 18 into the atmosphere. Someof the recycle air 19 can be branched off before the mill, beingrecombined with the product stream as a by-pass 20 at the end of themill. This assists pneumatic delivery of the material discharged inknown manner and provides for the necessary wind velocity in theseparator. The quantity of gravel accumulating in the separator can bepredetermined by suitably distributing the quantities of air passingthrough the mill and through the by-pass. By virtue of this measure,coupled with the setting of the separator, it is possible to determinethe continuously accumulating quantity of gravel which passes over themagnetic separator so that the efficiency with which the magnetizablecomponents are separated is also governed thereby.

The process according to the invention is illustrated in the followingExamples:

EXAMPLE 1 Most of the metallic iron present in a titanium slagcontaining up to 1 percent of metallic Fe was removed in order to avoiddifficulties during further processing.

a. Removal from the unground titanium slag by means of a drum-magnetseparator (drum rotating at 150 r.p.m.)

% output of Fe metal b. Removal from the gravel return of the grindingmachine by means of a drum-magnet separator (drum rotating at 176r.p.m.)

Non- Gravel return magnetic Magnetic used fraction fraction Weight [kg]25.660 27.735 0.925 by weight 100.0 96.4 3.6 Grain distribution 150;.t18.2% 16.7% 31.4% 150-100;t 19.7% 20.6% 10.2% -60p. 33.8% 35.4% 20.3%60-40;; 13.1% 14.5% 13.3% 40;1. 15.2% 12.8% 24.8% Analysis TiO, 70.171.0 4.5 Fe metal 3.48 0.23 90.60 Weight of Fe metal 0.894 kg 0.057 kg0.837kg output of Fe metal 93.7%

c. Removal from the fine material by means ofa magnetic separator Non-Fine material magnetic magnetic used fraction fraction Weight [kg] 5.5345.490 0.044 by weight 100.0 99.2 0.8 Grain distribution 40,1 16.3% 16.1%15.4% 401.1. 83.7% 83.9% 84.6% Analysis TiO, 70.6 70.9 39.2 Fe metal0.67 0.34 41.3 Weight of Fe metal 0.037 kg 0.019 kg 0.018 kg output ofFe metal 49% EXAMPLE 2 The effectiveness of magnetic separationfollowing enrichment of the Fe metal in the gravel return of thegrinding machine by adjusting the separator accordingly is demonstratedin the following Examples. A titanium slag containing 0.7 percent of Femetal was ground in a continuously fed industrial grinding and dryingmachine. Drum-magnet separators were used for magnetic separation. Ineach case, the drums rotated at 180 rpm.

Ratio by weight of gravel return to fine material 2.2-fold 0.l5-fold Femetal in the unground titanium slag 0.7% 0.7% Fe metal in the gravelreturn 3.4% 4.8% Enrichment of the Fe metal content in the gravel return49-fold 6.9-fold Fe metal in the magnetic fraction 58.8% 76.4%Enrichment of the Fe metal content in the magnetic fraction as againstthe starting slag 84-fold l07-fold Fe metal in the fine material 0.20%O.l8% output of Fe metal 72% 75% EXAMPLE 3 After suitablepre-separation, a mixture prepared from ilmenite ore and rutile sand(grain sizes between 60 and 200p.) was divided into two fractions by asingle magnetic separation:

llmenite ore Rutile sand Loose weight 2.61 g/cc. 2.48 g/cc. Mixture: 100parts by weight of starting mixture made up of 65 parts 35 partsMagnetic separation: (at) 72 parts by weight of magnetic fraction made64 parts by 8 parts by up of weight 89% weight ll% (b) 28 parts byweight of v non-magnetic fraction 1 part by 27 pans by made up of weight4% weight 96% The results of chemical analysis in each case were asfollows:

Magn.

llmeniteRutile Mixture fraction Non-magn.

oresand 65 llm: 89% fraction 35 Ru. ilmenite 96% ore Ru-sand by weightof TiO, 50396.1 66.8 55.2 93.2 by weight of total Fe (present in theform of iron oxides) 35.70.28 23.4 31.9 1.8

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:

1. In the process of grinding ofa material, high in titanium dioxide andlow in iron, containing magnetizable particles to effect size reduction,the improvement which comprises pneumatically separating from the groundproduct a fraction of particles from between 5 to 400 11., separatingthis fraction by centrifugal air separation into titanium dioxideenriched particles of between 5 and a and iron enriched coarse particlesof between 30 and 400 [.L, collecting the titanium dioxide enrichedfines, subjecting the iron enriched coarse material to magnetic forcesto separate the magnetizable particles from the balance of the coarsematerial, and returning such balance for further grinding.

2. Process according to claim 1, wherein the initial material is wet andpneumatic separation is effected with warm air, whereby the fines aredried prior to collection.

3. Process according to cairn I, wherein the starting material comprisesan iron-containing titanium material.

4. Process according to claim 3, wherein said titanium materialcomprises a titanium ore.

5. Process according to claim 3, wherein said titanium materialcomprises a slag from the reduction of titanium ore.

q um' mn S'IA'IESPA'IEN'I OFFICE.

, CERTIFICA PL 01* CO RRECIION Patent No. 3,75 I I Dated August 28, 19736 Inventcn-(s) Gerhard Kienast et al I i It is certified that errorappears the aboye-identified patent and that said Letters Patent arehereby corrected as shown below:

C01. 5', lines 40 and 41, cancel in theit entirety.

Col. 6, rewrite table at top-of pageto read as follows:

Ilmenite Rutile Mixture Magn. fraction, Non-magn 01 e" sand 65 11111:89% ilmenite fraction 35 Ru. ore 96% Ru-sand by weight of TiO 50. 3 96.166.8 55.2 93.2 v by weight of total Fe (present in the form of ironoxides) 35.7 0.28 23. 4 31.9 1.8

Signed and sealed this 17th day of September 1974;

(SEAL) Attest: v

MCCOY M. GIBSON JR. 1 C. MARSHALL DANN Attesting Officer Commissioner ofPatents

2. Process according to claim 1, wherein the initial material is wet andpneumatic separation is effected with warm air, whereby the fines aredried prior to collection.
 3. Process according to caim 1, wherein thestarting material comprises an iron-containing titanium material. 4.Process according to claim 3, wherein said titanium material comprises atitanium ore.
 5. Process according to claim 3, wherein said titaniummaterial comprises a slag from the reduction of titanium ore.